1. Field of the Disclosure
The disclosure relates generally to mud pumps. More particularly, the disclosure relates to cylinder sleeves of mud pumps. Still more particularly, the disclosure relates to a replaceable cylinder sleeve, and applying radially compressive pre-load to the replaceable sleeve.
2. Background of the Disclosure
In extracting hydrocarbons from the earth, it is common to drill a borehole into the earth formation containing the hydrocarbons. A drill bit is attached to a drill string, and during drilling operations, drilling fluid, or “mud” as it is also known, is pumped down through the drill string and into the hole through the drill bit. Drilling fluids are used to lubricate the drill bit and keep it cool. The drilling mud also cleans the bit, balances pressure by providing weight downhole, and brings sludge and cuttings created during the drilling process up to the surface. Finally, the drilling fluid can reveal the presence of oil, gas or water that may enter the fluid from a formation being drilled and may reveal information about the formation through drill cuttings. A viscous drilling fluid is capable of transporting more and heavier cuttings, so viscous drilling fluid can be advantageous, and often additives are utilized to increase viscosity.
Slush or mud pumps are commonly used for pumping the drilling mud. The pumps used in these applications are reciprocating pumps typically of the duplex or triplex type. A duplex pump has two reciprocating pistons that each force drilling mud into a discharge line, while a triplex reciprocating pump has three pistons that force drilling mud into a discharge line. These reciprocating mud pumps can be single acting, in which drilling mud is discharged on alternate strokes, or double acting, in which each stroke discharges drilling mud.
The pistons and cylinders used for such mud pumps are susceptible to a high degree of wear during use because the drilling mud is relatively dense and has a high proportion of suspended abrasive solids. This translates into a relatively short lifetime of the cylinder and necessitates frequent replacement of the cylinder. As the cylinder in which the piston reciprocates becomes worn, the small annular space between the piston head and the cylinder wall increases substantially and sometimes irregularly. This decreases the efficiency of the pump. To counteract the effect of this wear, mud pumps typically utilize of an expendable cylinder liner apparatus.
The general construction of a mud pump cylinder liner apparatus involves using three pieces of tubular material: a sleeve, a hull, and a collar. The sleeve forms the inside surface of the liner apparatus, the hull is assembled by shrink fit over the sleeve, and the collar is a flange ring that is shrink fit around the hull and normally retains the liner apparatus in the mud pump cylinder. The shrink fit between the sleeve and the hull creates a mechanical radial compressive pre-load on the sleeve and serves to counteract the effects of the alternating axial compressive forces and internal pressures on the cylinder sleeve which can lead to fatigue and failure of the cylinder sleeve and necessitate the replacement of the cylinder liner apparatus.
FIG. 1 illustrates an embodiment of a prior art cylinder liner apparatus 10 and includes clamping collar 20, cylinder hull 30, and sleeve 40. A central axis 15 passes through the longitudinal center of cylinder liner assembly 10. Annular clamping collar 20 is centered about central axis 15 and includes a collar bore 22 having an inner diameter 24. Cylinder hull 30 is concentrically disposed within collar bore 22 of clamping collar 20 to secure apparatus 10 to a fluid side of an existing mud pump module. Cylinder hull 30 includes a hull wall 32 having an outer diameter 34 and a hull bore 36 having an inner diameter 38. Further, hull wall 32 outer diameter 34 is larger than inner diameter 24 of collar bore 22 in clamping collar 20. Sleeve 40 is concentrically disposed within cylinder hull 30. Further, sleeve 40 includes a sleeve wall 42 with an outer diameter 44 that is larger than inner diameter 38 of cylinder bore 36 in cylinder hull 30, and an inner bore 41 for receiving the pump piston.
The motion of the reciprocating pump piston subjects the cylinder sleeve to alternating axial forces and internal pressures. The alternating internal pressures translate to alternating radial stresses in the cylinder sleeve that can lead to metal fatigue from the cyclic loading and sudden changes in direction of the piston motion. To counteract the effects of fatigue, radial compressive pre-load is applied to the cylinder sleeve such that the alternating internal pressure creates less fatigue stress in the sleeve than a sleeve with no pre-load. The radial compressive stresses are critical to ensure that the sleeve resists cyclic fatigue due to the cyclic pressures of the operating pump.
The method of imparting radial compressive pre-load using the prior art cylinder liner apparatus 10 includes heating cylinder hull 30 until inner diameter 38 of hull bore 36 is greater than outer diameter 44 of sleeve 40, then inserting sleeve 40 into hull bore 36. Next, cylinder hull 30 is cooled causing cylinder hull 30 to contract and decrease inner diameter 38 and radially contact and compress sleeve 40. Then, clamping collar 20 is heated until inner diameter 24 of collar bore 22 is greater than outer diameter 34 of outer wall 32. Cylinder hull 30 is inserted into collar bore 22, and clamping collar 20 is cooled to cause clamping collar 20 to contract and decrease inner diameter 24 and radially contact cylinder hull 30. Such a shrink fit cylinder liner assembly is complex and costly to manufacture. Further, the entire cylinder liner assembly 10 is discarded when only sleeve 40 wears out, thereby also adding to costs.
Accordingly, there remains a need in the art for cylinder liners that address the foregoing difficulties and overcomes other limitations of the prior art.